1. Field of the Invention
The present invention relates to a rolling bearing. In particular, the present invention relates to a rolling bearing which is a deep groove ball bearing having low torque and used for transmission support shafts or continuously-variable-transmission (CVT) shafts of hybrid vehicles (HVs).
2. Description of Related Art
Hybrid vehicles (HVs) have good fuel efficiency, and have become widespread in recent years. Rolling bearings used for transmission support shafts of the HVs are deep groove ball bearings which are suitably used with low torque. Rolling bearings used for continuously-variable-transmission (CVT) shafts are similarly deep groove ball bearings. The deep groove ball bearing includes an outer ring which serves as an outer bearing ring, an inner ring which serves an inner bearing ring, a plurality of balls, and a cage which is made of resin and holds the balls. The balls are rolling elements disposed between the outer ring and the inner ring and allowed to roll.
The rolling bearing used for the support shafts is disposed in lubricating oil in the transmissions or the CVTs. When the lubricating oil has a high oil level, agitation resistance of the oil is increased with the rotation of the rolling bearing, which causes torque loss. The oil level of the lubricating oil needs to be lowered to reduce the agitation resistance. In order to achieve this, the lubricating oil is required to smoothly flow through portions of the cage and the balls that are between the outer ring and the inner ring of the rolling bearing.
FIG. 8 shows a rolling bearing 100 disclosed in Japanese Patent Application Publication No. 2009-281585 (JP 2009-281585 A). In this rolling bearing 100, balls 106 are disposed between an outer ring 102 and an inner ring 104 and allowed to roll in deep grooves. In the rolling bearing 100, the balls 106 are held by a snap cage 108 which is made of resin. The snap cage 108 has an inner circumferential surface 108A in a radial direction. The inner circumferential surface 108A is a tilted surface and tilted such that the bore diameter of the cage 108 increases from the right side toward the left side as shown in FIG. 8. In the cage 108 having the tilted inner circumferential surface 108A and formed in such a tapered shape, lubricating oil flows well from the right side to the left side in FIG. 8 between the outer ring 102 and the inner ring 104, with the aid of centrifugal force. Accordingly, discharge efficiency of the lubricating oil is improved. This can lower the oil level of the lubricating oil, thereby reducing the agitation resistance of the lubricating oil.
In the case of the rolling bearing 100 shown in FIG. 8, the lubricating oil flows well from the right side to the left side. This configuration, however, is not effective in the case where the lubricating oil flows in the opposite direction, namely from the left side to the right side. That is, the configuration of the rolling bearing 100 is effective only when the lubrication oil flows in a certain direction.
In the conventional rolling bearing, in a case where efficiency with which lubricating oil flows in a rolling bearing is influenced by directions in which the lubricating oil flows, the rolling bearing needs to be installed in a device in consideration of the orientation of the rolling bearing. Such installation will be inconvenient. Accordingly, there is a demand for a rolling bearing which allows lubricating oil to flow well with similar efficiency in both directions so that the rolling bearing can be installed in a device without consideration of the orientation of the rolling bearing. There is also a demand for a rolling bearing in which lubricating oil flows well in both directions in a case where the lubricating oil flows in the rolling bearing in both directions.